This invention relates to thermostatic electrical switches and is particularly concerned with a time delay relay (TDR) utilizing a thermostatic switch assembly for opening and closing an electric circuit.
A relay of this type is the subject matter of U.S. Pat. No. 3,858,140 which comprises a thermally responsive switch adapted to make and break an electrical circuit mounted within a chamber of a time delay housing. A heater energized by a second circuit is positioned in heat transfer relation with the switch for heating a thermostatic element in the switch to thereby control the engagement and disengagement of electrical contacts in the switch. The heater and the switch and mounted within the chamber, terminals for energizing the heater are received in slots in the housing and a cover is placed over the chamber which engages the terminals to retain them in the housing. A retaining element interacts with the housing to hold the cover, switch, heater and terminals in assembled position.
Although relays made in accordance with the teachings of this patent have been very successful there are certain inherent characteristics of the structure which limit its usefulness for certain applications calling, for example, for devices having a faster response time or for devices which are less expensive to produce. For example, the one piece housing shown in the patent is a relatively massive member which tends to act as a heat sink and thereby to slow down the reaction time of the thermostatic switch. Since the housing is somewhat massive, it uses a relatively large amount of electrically insulative material adding to the material cost of the device. Further, the housing employs a separate cover of complex configuration as well as a spring retaining element. It has further been found in practice that after the retaining element is placed over the cover member it is frequently preferred to lock it in place with epoxy resulting in extra time required to assemble the device to allow for curing of the epoxy.
It is therefor an object of the present invention to provide a time delay relay having a very fast response time. Another object of the invention is the provision of a relay which has an inherently lower cost than prior art relays. Yet another object is the provision of a relay whose structure is such as to be particularly well suited to mass assembly line techniques. Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.
Briefly, a time delay relay of this invention comprises a housing formed of two identical shells formed with a plurality of grooves and a recess all open from a single direction. The shells have a back, bottom and top walls of generally the same thickness. Two opposite side walls have a free distal end portion forming an edge surface with a terminal receiving groove formed therein and extending through one of the top and bottom walls and having a notch adjacent the bottom wall. The edge surface of one of the side walls is formed with a joining groove and the edge surface of the other with a joining rib. First and second shelves extend from the back and side walls into the recess. A first elongated generally flat terminal member is received in one of the terminal receiving grooves of one shell and has a finger bent back upon itself received through the notch in the respective side wall and finger having a free distal end portion disposed between the first and second shelves. A second generally flat terminal member is received in the other of the terminal receiving grooves of same shell and has a finger extending through the notch in the respective side wall, the finger having a free distal end portion disposed in the recess. A thermostatic switch has a cup shaped metallic cap member mounted at its lower end with the outer periphery forming an annular berm received between the shelves in the same shell with the free distal end of the finger of the first terminal member in engagement with the berm or outer periphery of the cap member. The free distal end of the finger of the second terminal member is in engagement with a contact layer on one side of an electrical resistor element disposed on the cap member. The terminals and the switch extend out of the first shell and the switch is aligned with an aperture formed in the top wall. The other shell is placed over the first with the first terminal member received in the second terminal receiving groove of the other shell and the second terminal member received in the first terminal receiving groove of the other shell. The two halves are bonded together with the recesses forming a cavity in which the thermostatic switch is suspended.
According to a feature of the invention the terminal receiving grooves have spaced abutments to cooperate with tabs formed on the terminals to properly locate the terminals within the grooves. The terminals can extend outwardly either through the top or bottom wall as desired by extending the groove through the respective top or bottom wall.
Preferably the joining groove is formed with a wider mouth portion and the joining rib has a width greater than the joining groove but less than the mouth portion and a height less than the depth of the joining groove to facilitate ultrasonic soldering of the shells together.
According to a feature of the invention a manual reset function can be provided by forming a generally U-shaped platform with a button receiving bore in its bight and two downwardly projecting legs. Each leg has a groove generally equal to the thickness of the top wall adjacent its free distal end. A reset slide member extending through the top wall of the thermostatic switch has a tab which is received in a slot formed in the bottom of the button. The switch is placed in the recess with the platform placed over the aperture in the top wall of the first shell with the top wall received in a portion of the grooves in the legs. The second shell is then placed on the first with the top wall first with the top wall received in the remainder of the grooves in the legs to lock the platform in place.